Method of forming a high-k film on a semiconductor device

ABSTRACT

According to the present invention, high-k film can be etched to provide a desired geometry without damaging the silicon underlying material. A silicon oxide film  52  is formed on a silicon substrate  50  by thermal oxidation, and a high dielectric constant insulating film  54  comprising HfSiOx is formed thereon. Thereafter, polycrystalline silicon layer  56  and high dielectric constant insulating film  54  are selectively removed in stages by a dry etching through a mask of the resist layer  58 , and subsequently, the residual portion of the high dielectric constant insulating film  54  and the silicon oxide film  52  are selectively removed by wet etching through a mask of polycrystalline silicon layer  56 . A liquid mixture of phosphoric acid and sulfuric acid is employed for the etchant solution. The temperature of the etchant solution is preferably equal to or lower than 200 degree C., and more preferably equal to or less than 180 degree C.

This application is a divisional of U.S. application Ser. No. 10/854,306filed May 27, 2004 which is based on Japanese patent application No.2003-163017, filed Jun. 6, 2003, the content of which is incorporatedhereinto by reference.

FIELD OF THE INVENTION

The present invention relates to a semiconductor device comprising ametal compound film on a semiconductor substrate and manufacturingmethod thereof.

BACKGROUND OF THE INVENTION

In recent years, utilizations of a higher dielectric constant thin filmcalled high-k film for the application of a material composing of asemiconductor device are investigated. Typical high-k materials includeoxides containing Zr, Hf or the like. Novel superior device performancescan be achieved by employing such materials for a gate insulating filmof MOSFET and a capacity film of a capacitance element.

JP-A-2003-8004 (paragraphs [0026] to [0029] and FIG. 1) describes aMOSFET having a gate insulating film of a multi-layered structure(Al₂O₃—HfO₂—Al₂O₃) comprising aluminum oxide films formed on both of anupper and a bottom surfaces of a hafnium oxide film. When the high-kmaterial is employed for a gate insulating film of a transistor, thinnerfilm thickness converted into the silicon oxide film may be applicableeven if the thickness of the gate insulating film is designed to bethicker in a certain level, thereby providing the gate insulating filmwhich is physically and structurally stable.

In the preparations for forming the transistor comprising such gateinsulating film, it is necessary to remove gate insulating films formedin regions where gate electrode is not formed after the gate electrodeis fabricated. If this gate insulating film is not removed to remainthereon, the undesired short-channel effect may be remarkable, therebyreducing the reliability of the transistor.

Nevertheless, the hafnium oxide film is generally difficult to beetched. In the above-described patent application, it is described thatthe gate insulating film can be etched off by conducting reactive ionetching (RIE), and it is also described therein that if it is notsufficient with RIE, plasma etching may be employed. However, inreality, it is not easy to remove hafnium oxide film by conducting thedry etching. In particular, it is necessary to conduct a thermalprocessing at relatively higher temperature in the step for annealingthe gate electrode or the like during the manufacturing process for theMOSFET. During this step, crystallization of the hafnium oxide film iscaused to further convert the hafnium oxide film into a film that ismore difficult to be etched.

In addition, when the hafnium oxide film is dry etched, there might be aproblem of plasma damage to an underlying material of the high-kmaterial. In addition, silicon substrate is undesirably etched by thedry etching of the hafnium oxide film to vary the junction depth of theimpurity diffusion layer of the transistor, thereby increasing theleakage current therefrom.

On the other hand, even if the hafnium oxide film is to be removed viathe wet etching, the removal thereof may not easily be carried out. Suchcircumstances are described in No. 50 Extended Abstracts, Japan Societyof Applied Physics and Related Societies (Oyo Butsurigaku Kankei RengoKoenkai Koen Yokoshu), No. 2 (issued Mar. 27, 2003, at KanagawaUniversity), p.p. 934 (29a-ZW-5), entitled “Wet etching of HfO₂ byirradiating ultra-violet ray (Shigaisen-o shosha suru HfO₂ no wetetching)”, and it is described in the literature that the hafnium oxidefilm is difficult to be etched off and it is also described that theetching thereof becomes possible if the wet etching of such film withphosphoric acid under the exposure to the UV light is conducted.Conversely, there is nothing more difficult film for being etched offthan the hafnium oxide film so that such special processing must beconducted.

In addition, it is critical that the surface of the silicon substrate asan underlying material should not be damaged when the etching isconducted in the case of carrying out the wet etching. As describedearlier, it is general to form a silicon thermal oxide film between thefilm consisting of high-k material and the substrate, and an etchantavailable for etching the hafnium oxide film may also ordinarily etchthe silicon thermal oxide film, so that these films are simultaneouslyremoved with the identical etchant, and eventually the surface of thesilicon substrate is exposed. When such process is adopted, siliconsubstrate is readily damaged. Such problem is similarly occurred whensilicon native oxide film is chemically formed during a process step forcleaning the substrate employing a sulfuric acid-hydrogen peroxidemixture (SPM) and/or an ammonia-hydrogen peroxide mixture (APM), inaddition to the case of forming the silicon thermal oxide film.

Further, in the case of wet etching, a device isolating film of shallowtrench isolation (STI) structure is exposed to the surface by theetching, and thus problems of causing dissolution and/or damage of theexposed device isolating film may be caused when the above-describedetchant is used. This is because the device isolation film is ordinarilyconstituted of a silicon oxide film, which is readily dissolved by usingthe etchant available for etching the hafnium oxide film.

SUMMARY OF THE INVENTION

In view of the above situation, the present invention provides asolution to the above described problems, and it is an object of thepresent invention to provide a technology for etching a high-k film toprovide a desired geometry thereof without damaging an underlyingsilicon substrate material.

According to one aspect of the present invention, there is provided amethod for manufacturing a semiconductor device, comprising: forming ametal silicate film on an underlying material containing silicon, themetal silicate film containing, as main chemical elements, silicon,oxygen and one, two or more of metallic element or elements selectedfrom the group consisting of Hf, La, Zr and Al: and removing the metalsilicate film to expose the underlying material, wherein the metalsilicate film is removed during the removal of the metal silicate filmby employing a chemical liquid solution containing an oxidizing acid ora salt thereof.

According to another aspect of the present invention, there is provideda method for manufacturing a semiconductor device, comprising: forming agate insulating film comprising a metal silicate film on an underlyingmaterial containing silicon, the metal silicate film containing, as mainchemical elements, silicon, oxygen and one, two or more of metallicelement or elements selected from the group consisting of Hf, La, Zr andAl: forming a gate electrode film on the gate insulating film;selectively removing the gate electrode film to process thereof to ageometry of a gate electrode and to expose the metal silicate film; andremoving the metal silicate film to expose a surface of the underlyingmaterial, wherein the metal silicate film is removed during said removalof said metal silicate film by employing a chemical liquid solutioncontaining an oxidizing acid or a salt thereof.

As described earlier in the section of the prior art, the high-k filmcontaining refractory metal such as hafnium or the like is generallydifficult to be etched. On the contrary, the present invention employs aconfiguration, in which the metal silicate film is formed in place ofsuch metal film and the formed film is etched off by using an oxidizingacid or a salt thereof, so that the etching processing for theconfiguration, which has been difficult in the conventional technology,is facilitated to be carried out, thereby enabling a stable formation ofthe semiconductor device comprising the high-k film. The metal silicatefilm may be formed by various methods, and it is preferable to employ amethod of introducing silicon by using a silicon containing gas duringthe formation of the film. This configuration provides introducingsufficient quantity of silicon into the films, such that the removingwith the above-described chemical liquid solution becomes possible. Theremoving process with the chemical liquid solution may be conducted in amanner of, for example, dissolving of the metal silicate film to removethereof. Molar ratio (Si/(Si+Hf)) of silicon and hafnium in the metalsilicate film may preferably be equal to or higher than 5%, and morepreferably equal to or higher than 10%. This configuration providesbetter etch performances with higher stability.

In addition, according to the present invention, the oxidizing acid orthe salt thereof is employed as described above for removing the metalsilicate film to expose the underlying material containing silicon, andtherefore the level of the damage to the underlying material can bereduced to the minimum level. Here, “underlying material containingsilicon” indicates a silicon substrate itself or a silicon substratehaving a film formed thereon and having an uppermost surface comprisinga silicon-containing film. The silicon-containing film may includesilicon oxide film, silicon nitride film, silicon oxynitride film or thelike.

The method for manufacturing the semiconductor device according to thepresent invention may have a configuration, in which a device isolationfilm including a silicon oxide film having shallow trench isolation(STI) structure is formed on the underlying material and the deviceisolating film is exposed when the metal silicate film is removed toexpose the underlying material.

Since the device isolation film is ordinarily composed of silicon oxidefilm, problems of the dissolving and/or the damage may be occurred byusing the above-described etchant. On the contrary, the presentinvention employs the oxidizing acid or the salt thereof, such that thedamage to such a device isolation film can be reduced to the minimumlevel.

According to further aspect of the present invention, there is provideda method for manufacturing a semiconductor device, comprising: forming ametal silicate film on an underlying material containing silicon, themetal silicate film containing, as main chemical elements, silicon,oxygen and one, two or more of metallic element or elements selectedfrom the group consisting of Hf, La, Zr and Al: and removing the metalsilicate film to expose the underlying material, wherein the metalsilicate film is removed during the removal of the metal silicate filmby employing a chemical liquid solution containing an organic solventand hydrofluoric acid or a salt thereof.

According to yet other aspect of the present invention, there isprovided a method for manufacturing a semiconductor device, comprising:forming a gate insulating film comprising a metal silicate film on anunderlying material containing silicon, the metal silicate filmcontaining, as main chemical elements, silicon, oxygen and one, two ormore of metallic element or elements selected from the group consistingof Hf, La, Zr and Al: forming a gate electrode film on the gateinsulating film; selectively removing the gate electrode film to processthereof to a geometry of a gate electrode and to expose said metalsilicate film; and removing the metal silicate film to expose a surfaceof the underlying material, wherein the metal silicate film is removedduring the removal of the metal silicate film by employing a chemicalliquid solution containing an organic solvent and hydrofluoric acid or asalt thereof.

According to these aspects of the present invention, the metal silicatefilm is removed by using the chemical liquid solution comprising acombination of the organic solvent and hydrofluoric acid. Thus, thehandleability of the chemical liquid solution is improved. In addition,the high-k film can be etched to provide a desired geometry withoutdamaging to the silicon underlying material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are schematic cross sectional views of a semiconductordevice, showing manufacturing steps for the semiconductor deviceaccording to an embodiment of the present invention.

FIGS. 2A to 2D are schematic cross sectional views of a semiconductordevice, showing manufacturing steps for the semiconductor deviceaccording to an embodiment of the present invention.

FIG. 3 is a schematic cross sectional view of a semiconductor device,showing a manufacturing step for a conventional semiconductor device.

FIGS. 4A to 4C are schematic cross sectional views of a semiconductordevice, showing manufacturing steps for the semiconductor deviceaccording to another embodiment of the present invention.

FIG. 5 is a table, describing the result of the evaluation obtained froman example 1.

FIG. 6 is a table, describing the result of the evaluation obtained froman example 1.

FIG. 7 is a table, describing the result of the evaluation obtained froman example 2.

FIG. 8 is a table, describing the result of the evaluation obtained froma comparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A chemical liquid solution available to be employed in the presentinvention contains an oxidizing acid or a salt thereof. The chemicalliquid solution may contain pure water. Having such configuration, thedamage of underlying material comprising silicon caused by the chemicalliquid solution can be more effectively inhibited.

The oxidizing acid or the salt thereof available to be employed in thepresent invention may preferably contain one, two or more selected fromthe group consisting of phosphoric acid, sulfuric acid, nitric acid,perchloric acid, periodic acid, permanganic acid and salts thereof andceric ammonium nitrate. Having such configuration, the metal silicatefilm can preferably be removed. In addition, the damage to the siliconunderlying material can be reduced to a minimum level.

When phosphoric acid is selected as the above-described acid, theetching of the metal silicate film can be more stably conducted.Further, a liquid mixture of phosphoric acid and sulfuric acid may beemployed to effectively inhibit the roughening of the surface of theunderlying silicon. This aspect will be described later in thedescription of the examples.

The temperature of the chemical liquid solution may preferably be equalto or lower than 200 degree C., and more preferably equal to or lowerthan 180 degree C. during the removal of the metal silicate film. Thelower limit of the temperature thereof may be, for example, 40 degreeC., and more preferably equal to or higher than 60 degree C. Having suchconfiguration, the metal silicate film can stably be removed whileinhibiting the roughening of the surface of the underlying silicon.

In the present invention, various types of films may be employed for themetal silicate film. More specifically, the metal silicate filmcontaining, as main chemical elements, silicon, oxygen and one, two ormore of metallic element or elements selected from the group consistingof Hf, La, Zr and Al may be employed, and among these, the filmcontaining hafnium particularly provide more remarkable effectobtainable by the present invention. By etching such film with thechemical liquid solution according to the present invention, the etchingcan stably be carried out with higher efficiency. Here, theabove-described metal silicate film may additionally contain nitrogen.

Methods for manufacturing a semiconductor device according to thepresent invention will be described as follows with reference to FIGS.1A to 1D and FIGS. 2A to 2D. The description thereof will be made byillustrating a method for manufacturing a transistor as follows.

First, as shown in FIG. 1A, a device isolation film 51 of the shallowtrench structure is formed on a silicon substrate 50, and then a siliconoxide film 52 (for example, film thickness 0.8 nm) is formed by athermal oxidation, and a high dielectric constant insulating film 54comprising HfSiOx (for example, film thickness 2.0 nm) is formedthereon, and further, a polycrystalline silicon layer 56 (for example,film thickness 200 nm) is formed thereon via chemical vapor deposition(CVD). The device isolation film 51 has a structure, in which a CVDsilicon oxide film is embedded in a trench formed on the siliconsubstrate 50.

Metal organic chemical vapor deposition (MOCVD) is employed as a methodfor forming the high dielectric constant insulating film 54 here.

Subsequently, as shown in FIG. 1B, a resist film is formed on thepolycrystalline silicon layer 56, and a resist layer 58 is formed byemploying a lithography technology utilizing an excimer laser.Thereafter, as shown in FIG. 1C and FIG. 1D, polycrystalline siliconlayer 56 and high dielectric constant insulating film 54 are selectivelyremoved in stages by a dry etching through a mask of the resist layer58. After conducting the etching to the halfway in the thickness of highdielectric constant insulating film 54, the resist layer 58 and theresidual matter are removed by a sulfuric acid-hydrogen peroxide mixture(SPM) and/or an ammonia-hydrogen peroxide mixture (APM) (FIG. 2A).

Subsequently, the residual portion of the high dielectric constantinsulating film 54 and the silicon oxide film 52 are selectively removedby a wet etching through a mask of polycrystalline silicon layer 56(FIG. 2B and FIG. 2C). The surface of silicon substrate 50 is exposed byconducting this procedure. A liquid mixture of phosphoric acid andsulfuric acid is employed for the etchant solution. The temperature ofthe etchant solution is preferably equal to or lower than 200 degree C.,and more preferably equal to or less than 180 degree C. The lower limitof the temperature is 40 degree C., for example, and more preferablyequal to or higher than 60 degree C.

Thereafter, the surface of the silicon substrate 50 is rinsed. In thisembodiment, after completing a first rinse step employing pure water orwarm water, a second rinse step employing isopropyl alcohol is carriedout. This removes moisture having remained on the surface of the siliconsubstrate 50, thereby preventing the formation of the watermarks on thesurface of the silicon substrate 50.

Subsequently, after conducting an ion implantation process for formingan extension region by a known technology, side walls 64 are formed, andthereafter, ions are implanted onto the surface of the silicon substrate50. This provides the formation of impurity regions 62 on both sides ofthe gate electrode containing polycrystalline silicon layer 56 (FIG.2D). Subsequently, a metal layer is formed on the entire surface of thesilicon substrate 50 (not shown), and a silicidation of a portion of themetal layer contacting with the polycrystalline silicon layer 56 and theimpurity region 62, and thereafter the other portion of the metal layeris removed to form a metal silicide layer in a gate electrode, a sourceand a drain region (not shown.) Here, polycrystalline SiGe layer can beemployed for the gate electrode, in place of the polycrystalline siliconlayer 56.

According to the present embodiment, silicon is introduced into thehafnium oxide film to form the silicate film, and phosphoric acid isemployed as an etchant solution, and further the temperature of theetchant solution is preferably selected, so that the hafnium type gateinsulating film can easily be etched off, thereby reducing the damage tothe surface of the substrate to a minimum level. In the process usinghydrofluoric acid or the like that has been conventionally used as anetchant solution, the surface of the silicon substrate 50 is damagedduring the step of FIG. 2C. In addition, as shown in FIG. 3, the deviceisolation film 51 is dissolved by the etching, and there may be aharmful result of causing an increase of leakage current or the like. Inthis embodiment, such problems can be solved. In addition, according tothis embodiment, the damage of the surface of the polycrystallinesilicon layer 56 composing the gate electrode can effectively beinhibited, and the reliability of the device can be improved from thispoint of view.

In addition, if moisture remains on the surface of the silicon substrate50 when ion implantation onto the surface of the silicon substrate 50 isconducted, watermark is formed to cause non-uniform condition for theion implantation. According to the method of this embodiment, such aproblem can be solved.

Although the silicon substrate 50 is exposed by the wet etching shown inFIG. 2B and FIG. 2C in this embodiment, the etching may be stopped atthe stage shown in FIG. 2B to leave the silicon oxide film 52 in theregions thereof other than the region just under of gate electrode.

In addition, although the present embodiment employs a configuration, inwhich the dry etching is conducted to the halfway in the thickness ofthe high dielectric constant insulating film 54 as shown in FIG. 1D andthereafter the remaining portion of the high dielectric constantinsulating film 54 and the silicon oxide film 52 are selectively removedby the wet etching (FIG. 2B and FIG. 2C), etching of the high dielectricconstant insulating film 54 may be conducted by only a wet etchingwithout employing a dry etching.

The present invention has been described on the basis of the preferredembodiment. It should be understood by a person having ordinary skillsin the art that the present embodiment is disclosed for an illustrationonly, and the various changes thereof are available and are within thescope of the present invention.

For example, although the high dielectric constant insulating film 54 isdeposited via MOCVD in the above-described embodiment, other method fordepositing films may be employed. For example, the solid phase diffusionmay be employed. By illustrating the deposition of hafnium silicate, ahafnium film is first deposited on, or in contact with, the surface ofthe silicon oxide film via physical vapor deposition (PVD.) After thedeposition, an oxygen annealing may be conducted to form hafniumsilicate (HfSiOx.) Alternatively, a silicate film containing nitrogencan be formed via a method employing a silicon oxynitride film as theunderlying layer, or a method of introducing nitrogen into an annealingatmosphere, or the like. In addition, the material for the highdielectric constant insulating film 54 is not limited tohafnium-containing silicate, and a metal silicate film containing ametal selected from the group consisting of La, Zr and Al may beemployed for the high dielectric constant insulating film 54.

Alternatively, after the deposition of the high dielectric constantinsulating film 54, a silicon nitride film may be formed thereon, or anitridation processing may be conducted for the upper portion of thehigh dielectric constant insulating film 54. Having such modifiedconfiguration, the leakage current through the gate insulating film caneffectively be reduced. The nitridation processing can be conducted by,for example, a plasma processing using a nitrogen-containing compoundsuch as N₂O, NH₃ or the like, after having formed the high dielectricconstant insulating film 54. In the nitridation processing, remoteplasma may preferably be utilized. The processing apparatus utilizingremote plasma may comprise a separated plasma generation chamberseparated from the processing chamber containing a substrate therein,comprising a gas inlet, a waveguide and a microwave applying means, andthe plasma generated in the plasma generation chamber is guided througha silica tube to the chamber containing the substrate therein. Theplasma processing for the substrate surface is conducted in theprocessing chamber. By adopting such a system, sufficient level of thenitridation can be achieved while inhibiting the damage to thesubstrate. Here, the wet etching employing a chemical liquid solutioncontaining an oxidizing acid or the like according to the presentinvention or a salt thereof is effective, even in the case describedabove where the nitridation layer is disposed on the surface thereof.

Although the silicon oxide film 52 is completely removed in the step ofFIG. 2C in the above-described embodiment, the film may totally orpartially be remained. FIGS. 4A to 4C show the steps thereof. As shownin FIG. 4A and FIG. 4B, the high dielectric constant insulating film 54may be etched off, and thereafter an ion implantation may be conductedunder the condition where the silicon oxide film 52 is remained on thesurface of the silicon substrate 50 to manufacture a transistor shown inFIG. 4C.

Although the high dielectric constant insulating film 54 is removed byusing the phosphoric acid type chemical liquid solution in theabove-described embodiment, other types of chemical liquid solutions maybe employed. For example, a chemical liquid solution containinghydrofluoric acid or a salt thereof with an organic solvent can beemployed. Having such configuration, the handleability of the chemicalliquid solution is improved, and in addition, the high-k film can beetched to provide a desired geometry without damaging to the siliconunderlying material. In this case, the preferable organic solvent mayhave a higher flash point in view of better handleability, and forexample, di- or tri-alkylene glycol monoalkyl ether type solvents may beemployed. More specifically, the preferable organic solvents includediethylene glycol monobutyl ether, diethylene glycol monomethyl ether,dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether,triethylene glycol monomethyl ether, tripropylene glycol monomethylether, tripropylene glycol monoethyl ether or the like. In addition,N-methylpyrrolidone (NMP), propylene carbonate, dimethylsulfoxide(DMSO), butyrolactone, dimethylacetamide, dihydrofurfuryl alcohol (THFA)or the like are available, in place of di- or tri-alkylene glycolmonoalkyl ether type solvent, and one of these or a mixture of not lessthan two of these may be employed. Although the second rinse steputilizing isopropyl alcohol is conducted after carrying out the firstrinse step utilizing pure water or warm water in the present embodiment,the rinse method is not limited thereto and various types of rinsemethods can be adopted. For example, only a rinse step utilizing purewater or warm water may be employed. Alternatively, the rinse step maybe carried out by utilizing a mixture of pure water with ammoniadissolved therein or a mixture of pure water with ammonia and hydrogen,both of which is dissolved therein. In this case, the rinse step maycomprise only the rinse step utilizing these rinse liquids, or mayfurther comprise an additional rinse step utilizing isopropyl alcoholthereafter.

In addition, although the formation of the transistor is described forillustrating the present invention in the above-described embodiment,the present invention may be applicable to the formation of acapacitance element. In particular, when doped polysilicon is employedfor the lower electrode and a capacitance having a multi-layeredstructure comprising a capacitance film of a high-k material and anupper electrode is formed thereon, etching of the capacitance film isdifficult and moreover, the damage to the underlying polysilicon causedin the etching process becomes a problem. The method according to thepresent invention provides a manufacturing of the capacitance havingsuch a structure with higher production yield and higher processstability.

EXAMPLES Example 1

HfSiOx was formed on a surface of a single crystalline silicon substrateby MOCVD. The thickness of the obtained HfSiOx was 4 to 5 nm. Thissample is called as “sample 1.” Mole ratio (Si/(Si+Hf)) of silicon andhafnium in the above-described silicate film was equal to or higher than5%.

As a comparative example, a single crystalline silicon substrate wasthermally processed to form a thermal oxide film on the surface of thesubstrate. The thickness of the obtained SiO₂ was 100 nm. This sample iscalled as “sample 2.”

Etching processes were carried out for the sample 1 and the sample 2 byusing the following chemical liquid solutions.

(i) 0.5% diluted hydrofluoric acid: at a room temperature;

(ii) Phosphoric acid: at 160 degree C.; and

(iii) Liquid mixture of phosphoric acid and sulfuric acid: at 160 degreeC.

Here, phosphoric acid and sulfuric acid employed in the examples werecommercially available products that are generally employed for thesemiconductor applications.

The duration time for the etching was set to one minute. The results ofthe etch rates for each of the samples and ratios among these etch ratesare shown in FIG. 5. It is clarified that the etching utilizing thechemical liquid solution containing phosphoric acid providesconsiderably improved etch ratio, which is defined as (etch rate ofHfSiO_(x))/(etch rate of SiO₂), as compared with the case of utilizingdiluted hydrofluoric acid (DHF.)

Further, surface roughness of the silicon substrate after the etchingwas also observed by using an atomic force microscope. The results arealso shown in FIG. 5. It is clarified that the addition of sulfuric acidinto phosphoric acid in the chemical liquid solution provides theimproved surface roughness. It is also known from the results of otherexperiments that the addition of sulfuric acid in phosphoric acid in thechemical liquid solution also provides the improved surface roughness ofthe polycrystalline silicon that composes the gate electrode. Here, themeasurements of the surface roughness in the experiments utilizing DHFwere not conducted, because enough selection ratios were not obtained.

Next, the etching processes were conducted by using phosphoric acid forthe above described sample 1 and sample 2 at various solutiontemperatures, and the etch rates corresponding to various solutiontemperatures were measured. The results are shown in FIG. 6. As long asthe measured ranges are concerned, it is clarified that lowertemperature provides further improved etch ratio, which is defined as(etch rate of HfSiO_(x))/(etch rate of SiO₂). Here, it was confirmedthat the etch rate for phosphoric acid at the room temperature wasconsiderably deteriorated in the measurements for samples 1 and 2.

Example 2

A sample 1 and a sample 2 were prepared similarly as in the example 1,and etching processes were conducted with the following chemical liquidsolutions. The etching temperature was set to the room temperature.Molar ratios of silicon and hafnium (Si/(Si+Hf)) in the above-describedsilicate films were not lower than 5%.

(i) Mixture solution containing hydrofluoric acid, butyl diglycol(diethylene glycol monobutyl ether; hereinafter abbreviated as BDG), andpure water, mixture ratio of hydrofluoric acid to pure water was 1:1;and

(ii) Diluted hydrofluoric acid.

The duration time for the etching was set to one minute. The results ofthe etch rates for each of the samples and ratios among these etch ratesare shown in FIG. 7. In FIG. 7, “HF (10%)” means that 50% HF aqueoussolution (i.e., mixing ratio of hydrofluoric acid to pure water was 1:1)was employed to obtain a solution having a HF concentration of 10% overthe entire etchant solution. “DHF (10%)” also means 10% HF aqueoussolution. It is clarified that the etching utilizing butyl diglycolsolution containing hydrofluoric acid provides considerably improvedetch ratio, which is defined as (etch rate of HfSiO_(x))/(etch rate ofSiO₂), as compared with diluted hydrofluoric acid (DHF.) In addition, itis also clarified that when the system utilizing butyl diglycol solutioncontaining hydrofluoric acid is employed, the surface roughness of thesilicon substrate after the etching is reduced.

Although the reason of obtaining better etching characteristics byemploying the etchant solution utilizing BDG in this example is notnecessarily clear, the reason may be presumed as follows. Components ofHF and HF2⁻ exist in the HF aqueous solution and the etch rate for thefilm depends on the ratio of these components. When an organic solventsuch as BDG or the like is added to the HF aqueous solution, theconcentration of HF2⁻, which contributes to the etching of the siliconthermal oxide film, is reduced. Thus, it is presumed that the etch ratefor the silicon thermal oxide film (SiO₂) deteriorates, and the etchratio, which is defined as (etch rate of HfSiOx)/(etch rate of SiO2), isimproved.

Comparative Example

The same etchant solution as used in Example 2 was employed to conductan evaluation for a hafnium oxide film as an etching object. In thiscomparative example, HfOx was formed via MOCVD on a surface of a singlecrystalline silicon substrate to a film thickness of 4 to 5 nm. Etchingprocesses over this type of films were conducted with the followingchemical liquid solutions. The etching temperature was set to the roomtemperature.

(i) Mixture solution containing hydrofluoric acid, butyl diglycol(diethylene glycol monobutyl ether; hereinafter abbreviated as BDG), andpure water, mixture ratio of hydrofluoric acid to pure water was 1:1;and

(ii) Diluted hydrofluoric acid

The duration time for the etching was set to one minute. The results ofthe etch rates for each of the samples and ratios among these etch ratesare shown in FIG. 8. In FIG. 8, “HF (10%)” means that 50% HF aqueoussolution (i.e., mixing ratio of hydrofluoric acid to pure water was 1:1)was employed to obtain a solution having a HF concentration of 10% overthe entire etchant solution. “DHF (10%)” also means 10% HF aqueoussolution. It is clarified that the hafnium oxide film can notsufficiently be etched by using the above-described etchant solution(i).

It is clarified from the results of Example 2 and Comparative Examplethat the etching ability considerably differs depending upon the type ofthe film to be etched when the etchant solution containing hydrofluoricacid, butyl diglycol and pure water is employed, and that the abovedescribed etchant solution specifically provides better etching abilityspecific to hafnium silicate.

According to the present invention, the high-k film can be etched toprovide a desired geometry without damaging an underlying siliconsubstrate material, and the semiconductor device including the high-kfilm as a structural component can stably be formed.

1. A method for manufacturing a semiconductor device, comprising thesteps of: forming a metal silicate film on an underlying materialcontaining silicon, said metal silicate film containing, as mainchemical elements, silicon, oxygen and one, two or more of metallicelement or elements selected from the group consisting of Hf, La, Zr andAl: and removing said metal silicate film to expose said underlyingmaterial, wherein said metal silicate film is removed during saidremoval of said metal silicate film by employing a chemical liquidsolution containing an oxidizing acid or a salt thereof that containsone, two or more selected from the group consisting of phosphoric acid,nitric acid, perchloric acid, permanganic acid, salts thereof and cericammonium nitrate.
 2. The method according to claim 1, wherein a deviceisolation film including a silicon oxide film having shallow trenchisolation (STI) structure is formed on said underlying material andwherein said device isolating film is exposed when said metal silicatefilm is removed to expose said underlying material.
 3. The methodaccording to claim 1, wherein said chemical liquid solution containspure water.
 4. The method according to claim 1, wherein said oxidizingacid contains phosphoric acid.
 5. The method according to claim 1,wherein said metal silicate film is removed at a temperature of saidchemical liquid solution within a range from 40 degree C. to 200 degreeC.
 6. The method according to claim 1, wherein said metal silicate filmis removed at a temperature of said chemical liquid solution within arange from 60 degree C. to 180 degree C.
 7. A method for manufacturing asemiconductor device, comprising the steps of: forming a gate insulatingfilm comprising a metal silicate film on an underlying materialcontaining silicon, said metal silicate film containing, as mainchemical elements, silicon, oxygen and one, two or more of metallicelement or elements selected from the group consisting of Hf, La, Zr andAl: forming a gate electrode film on said gate insulating film;selectively removing said gate electrode film to process thereof to ageometry of a gate electrode and to expose said metal silicate film; andremoving said exposed metal silicate film to expose a surface of saidunderlying material, wherein said metal silicate film is removed duringsaid removal of said metal silicate film by employing a chemical liquidsolution containing an oxidizing acid or a salt thereof that containsone, two or more selected from the group consisting of phosphoric acid,nitric acid, perchloric acid, permanganic acid, salts thereof and cericammonium nitrate.
 8. The method according to claim 7, wherein saidoxidizing acid contains phosphoric acid.
 9. The method according toclaim 1, wherein the group consists of nitric acid, perchloric acid,permanganic acid, salts thereof and ceric ammonium nitrate.
 10. Themethod according to claim 7, wherein the group consists of nitric acid,perchloric acid, permanganic acid, salts thereof and ceric ammoniumnitrate.